The invention relates to a method for identifying plural relations in a continuous sheet manufacturing process.
Plural actuators are commonly deployed across a sheet making apparatus in order to regulate one or more properties of the sheet in the cross machine direction. Sheet properties are commonly measured at a plurality of locations across the sheet, where such plurality of measurement locations across the sheet normally equals or exceeds the plurality of actuators. The effect of an actuator on a measured sheet property is referred to as the response of the actuator. The set of locations of the centres of responses for each actuator is referred to as the mapping for the actuators. Efficacy of the regulation of sheet properties in the cross machine direction by governing such actuators is determined for example by the accuracy of the mapping and response information employed by regulation means.
U.S. Pat. No. 5,400,258 discloses a method in which prior knowledge of the response shape is used in a pattern matching scheme for estimating mapping positions from the change to a measured profile caused by a bump test. In U.S. Pat. No. 5,539,634, the mapping is deduced from the effect on the apparent noise profile of a sheet property caused by cycling one or more actuators. In the above cases bump tests cause marks in the sheet. Further the prior art in this field requires that a method of identifying responses or mapping has exclusive governance over the actuators during the period of identification, e.g. it is required that no other excitation of the actuators occur during the excitation for purposes of identification.
Accordingly, it is an object of the present invention to provide an improved method for identifying sheet property relationships in a continuous sheet manufacturing process.
Preferably the present method comprises the steps of a) specifying a first time period to be used as the cycle time of a cyclic excitation, b) measuring a sheet property profile, c) calculating a reference pseudo-property profile from plural measurements of said measured sheet property profiles using a phase lag substantially equal to half of said first time period, d) applying a cyclic excitation pulse to at least one actuator, with a cycle time substantially equal to the first time period, e) measuring an excited sheet property profile, f) calculating an excited pseudo-property profile from plural measurements of the measured excited sheet profiles using a phase lag substantially equal to half of said first time period, and g) deducing properties of the sheet from the difference between said excited pseudo-property profile and said reference pseudo-property profile.